Explore chapters and articles related to this topic
Chemical Reaction Thermodynamics, Kinetics, and Reactor Analysis
Published in Debabrata Das, Debayan Das, Biochemical Engineering, 2019
For an endothermic reversible reaction, Keq increases with temperature, whereas for an exothermic reaction, Keq decreases with increasing temperature. The parameter Keq varies with temperature, which is further given by the van’t Hoff equation as follows: () logKeq2Keq1=ΔH2.303R(1T1−1T2)
Force-System Resultants and Equilibrium
Published in Richard C. Dorf, The Engineering Handbook, 2018
A reaction that proceeds by a mechanism involving more than a single reaction path or step is termed a complex reaction. Unlike elementary reactions, the mechanisms of complex reactions differ considerably from their stoichiometric equations. Most industrially important reactions are complex reactions, the mechanisms of which can often be determined by assuming that the overall reaction consists of several elementary reaction steps. The resulting overall rate expression is then compared with the experimental data, and the procedure is repeated until a desired degree of agreement is obtained. Each of the elementary reaction steps may proceed reversibly, concurrently, or consecutively. A reversible reaction is one in which conversion of reactants to products is incomplete at equilibrium because of an increasing influence of the reverse reaction as the forward reaction approaches equilibrium. For a reversible reaction of the type A+B⇔krkfD+E
Miscellaneous Algorithms
Published in Nazmul Siddique, Hojjat Adeli, Nature-Inspired Computing, 2017
Reversible reaction: In a reversible reaction, the chemical reactants form products that, in turn, react together to give the reactants back. Such reactions take place in both forward and backward directions under certain suitable conditions. An example of a reversible reaction is the calcium carbonate: CaCO3 ↔ CaO + CO2. Reversible reactions will reach an equilibrium point where the concentrations of reactants and products will no longer change.
Catalysts used in biodiesel production: a review
Published in Biofuels, 2021
A catalyst is a substance that increases the chemical reaction rate without being consumed by the reaction itself. Theoretically, the catalyst is practically consumed in one stage and regenerated at a later stage, and this operation is continuously repeated without imposing a permanent change on the catalyst. Accordingly, the catalyst in a given reaction can be recycled unchanged at the end of the reaction. Catalysts change the speed of a chemical reaction that can be thermodynamically carried out. Therefore, they cannot perform reactions that are not thermodynamically feasible. Basically, a catalyst is considered a chemical compound capable of applying an accelerating effect on the reaction rate and a directional effect on the reaction progression which is thermodynamic in nature. In a reversible reaction, the catalyst evenly affects the rate of forward and backward reactions. Therefore, the equilibrium constant of the reaction is the same whether in the presence of a catalyst or without it. When there are several mechanisms available for the reaction, the catalyst must be selected. In principle, the catalyst should increase the ratio of the desired material to the unwanted material. Although ideally catalysts remain unchanged during the reaction, this is inaccurate in practice, since the catalyst itself is a reactive substance that undergoes irreversible physical and chemical changes during the reaction, reducing its ability to function. Over time, this reality may be vividly observed since the catalyst enters into billions of reactions [5]. In general, the catalysts used in the transesterification of vegetable oils and animal fats can be classified into three groups – homogeneous, heterogeneous and enzymatic catalysts [12] – as shown in Figure 1.